Chronic pulmonary hypertension, whether primary or secondary, whether in adult or pediatric patients, is a debilitating and ultimately fatal disease for which there is no satisfactory treatment. Extensive examination of the pathological changes found in lungs from human and animal models has clearly indicated that alterations in vascular smooth muscle cells are involved. While numerous initiating stimuli have been described, there is little information about how these stimuli ultimately result in smooth muscle cell alterations. In the current proposal, lung lymph will be collected from sheep during the development of chronic pulmonary hypertension induced by air embolization. The lymph will be added to cultures of normal sheep lung vascular smooth muscle cells, and their proliferation and matrix production will be determined. Preliminary studies show that lymph from hypertensive sheep stimulates the proliferation of vascular smooth muscle cells in vitro. Additionally, smooth muscle cells from the lungs of sheep will be cultured during the development of pulmonary hypertension and their proliferative and synthetic behavior will be characterized first in standard media and then in the presence of media containing normal and hypertensive lymph. Preliminary data suggest that "hypertensive" cells maintain an altered phenotype in culture. Using well established cell biological techniques to study the smooth muscle cells in their environment (lung lymph) and using the extensive knowledge that is available about the control of cell growth, the proposed experiments will provide insight into the factors/mechanisms operative in the development of chronic pulmonary hypertension. A better understanding of the mechanisms could lead to therapy or prevention of this devastating disease.